This invention relates to an electrosatic filter with a process for fast cleaning without breaking confinement.
Electrostatic filters are composed of electricity conducting elements brought to different voltages by means of a DC voltage generator. Powerful electrostatic charges are created between these elements, between which a gas current passes carrying dust: particles making up this dust, ionized naturally or after a prior operation, are attracted by the conducting elements and deposited on them. Electrostatic filters have proved to be very useful for purifying gases containing large quantities of impurities such as combustion gases; they are frequently used on the inlet side of very high efficiency filters which retain the finest particles but which would become dirty too quickly if the gases reached them directly.
However, it is inevitable that electrostatic filters also become dirty, despite the relatively large gaps between conducting elements, so that cleaning processes are provided.
Brushes or scrapers are usually used that are applied along the length of the conducting elements, but this significantly complicates the filter. One possibility that was considered was to separate accumulated impurities by vibrations, by shaking or applying shocks on the sides of conducting elements, but this requires a large amount of energy and it is not always easy to determine the optimum conditions for vibrations to clean efficiently, and in any case mechanical vibrations could damage the filter.
Ultrasonic transducers are used in patent FR-A-2,638,659, through openings in the filter enclosure. These transducers are terminated by a rigid metal ground acting as an ultrasound emitter. This design can only be satisfactory in an aqueous environment, and therefore is not suitable for removing dust from gas.
Note also the author's certificate SU-A-927,317, in which cleaning is done by brushes and a reversal of the electrostatic field and in which detached particles are guided by sirens, the acoustic waves from which are propagated in the filter without contributing directly to cleaning. The sirens are engaged in the filter without being separated from filter elements by any membrane or partition, which compromises the confinement. Finally, the sirens must operate continuously during cleaning, and the resulting noise level is very annoying.